Hepatocarcinogenesis represents an ongoing process which could be divided in initiation and promotion. In the course of promoting phase, a number of focal cell populations have been identified as putative precursors of ultimately emerging neoplastic cells. Our studies showed that sex hormonal environment modifies the emergence of hepatic nodular lesions even when acting following carcinogenic treatment. This led to hypothesis and androgen/estrogen ratio modulates incidence of livers tumors by influencing temporal emergence or progression of the progency of the initiated cells through the precursor cell populations: high ratio accelerating while low ratio delaying their progression to neoplastic state. In previous studies we have identifield single dose levels of diethylnitrosamine (DEN) which were effective to induce focal cellular changes and a broad spectrum of nodula liver lesions including hepatocellular carcinomas in direct relationship to dose used. In order to determine the histogenesis of hepatocellular carcinomas in the mouse and to test the above hypothesis regarding hormonal role in hepatocarcinogenesis, we intend to apply a variety of qualitative and quantitative histochemical and autoradiographic techniques to our well-defined animal model. Both intact and gonadectomized mice will be used. Temporal progression of focal putative preneoplastic lesions, identified by their newly expressed phenotypic characters, will be monitored throughout post-initiating phase of hepatocarcinogenesis, utilizing histochemistry (glucose-6-phosphatase, alkaline phosphatase, gamma-glutamyltranspeptidase, glycogen, beta-glucuronidase), autoradiography (labelling index) and radioimmune assay (serum alpha-fetoprotein).